Portable telephone

ABSTRACT

A digital portable radio having a plane antenna, which minimizes the area of a board occupied by a built-in antenna without deteriorating gain. More specifically, a built-in antenna radiation element having a conductor capable of being electrically connected to a power feed circuit provided on the circuit substrate is fixed on the internal wall of the casing. A built-in antenna which accomplishes high gain and occupies a small area is obtained. Further, the antenna radiation element is formed from a metal plate and has a branch where one end of a longer radiation element formed from a thin metal plate is connected to one end of a shorter radiation element, and the other end of each of the radiation elements is open. Further, gap is formed by bringing the open end of the longer radiation element in close proximity to the open end of the shorter radiation element. Impedance matching is accomplished by utilization of coupling capacitance developed in the gap. The antenna radiation element becomes a quarter λ non-grounding multiple resonance built-in antenna by feeding of power to the branch. This antenna is fitted on the internal wall of the casing of the portable radio.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a portable radio, such asprimarily a digital portable telephone having a built-in plane antenna,and more particularly to the space-saving structure of the built-inantenna. Further, the invention relates to a plane antenna which ismainly used in a digital portable radio (a portable telephone).

[0002] A plane antenna has been widely used as a built-in antenna of adigital portable telephone because of its advantages of compactness andhigh gain. The built-in antenna of the portable telephone is directlymounted on a circuit substrate.

[0003] In recent years, a portable telephone market has spread into wideuse, and the portable telephone is miniaturized so as to sufficientlyfit in a pocket. The portable telephone tends to be miniaturizedfurther. In conjunction of miniaturization of the portable telephone,there is also a demand for a reduction in the space occupied by thebuilt-in antenna attached to the portable telephone.

[0004] However, if the size of the portable telephone is reducedfurther, it becomes difficult to ensure space for the built-in antenna.This is because as the size of the case is reduced, a circuit originallymade up of a plurality of circuit boards is constituted of only oneboard. In addition, the circuit board itself becomes more compact. Forthese reasons, the electronic components are mounted on the circuitboard in high density. Accordingly, the space required to mount thebuilt-in antenna on the board is reduced, the antenna must be formed insmall size. In general, a small-sized antenna entails the deteriorationof gain, which in turn may result in a drop in the performance of theportable telephone. However, if an attempt is made to increase the sizeof the built-in antenna, it becomes impossible to store an electroniccircuit in the case.

[0005] Aside from the foregoing problem, there is a lot of talk aboutthe problem related to a line. More specifically, the frequency ofutilization of a line is increased in proportion to an increase in thenumber of portable telephones, and traffic becomes nearly full. Thenumber of circuit lines is increased by utilization of a frequency rangeof the analog portable telephone as measures against the increase in thetraffic. However, this method requires two receiving ranges. It isimpossible to provide an existing built-in antenna having a narrow rangewith the sensitivity which covers two ranges. Therefore, there is neededan antenna which produces two resonance ranges (or multiple resonance)and has sensitivity over two ranges.

SUMMARY OF THE INVENTION

[0006] To solve the foregoing problem and to minimize the area occupiedby a board of a built-in antenna without deterioration of a gain, aradiation element of a built-in antenna is mounted on an internal wallof a case, and a conductor is provided which is capable of electricallyconnecting the radiation element to a power feed circuit provided on theboard, thereby providing a built-in antenna which achieves high gain andrequires the space occupied by the circuit board.

[0007] To ensure sensitivity over to receiving ranges, an antennaradiation element is provided with a branch where one end of a longerradiation element is connected to one end of a shorter radiationelement. The other ends of the longer and shorter radiation elements areopen ends and are positioned in close proximity to each other so as toform gap between them. Impedance matching is accomplished by means ofthe mutual coupling capacitance developed in the gap, and power is fedto the branch.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a side cross-sectional view showing a portable radioaccording to a first embodiment of the present invention;

[0009]FIG. 2 is a side cross-sectional view showing a portable radioaccording to a second embodiment of the present invention.

[0010]FIG. 3 is a front view showing an antenna radiation elementaccording to the third embodiment of the present invention; and

[0011]FIGS. 4A to 4C are plots showing the characteristics of theantenna according to present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Embodiments of the present invention will be described hereinbelow.

Embodiment 1

[0013]FIG. 1 is a side cross-sectional view showing a case of a portableradio according to the present invention. In FIG. 1, a portion of thecase located in an upper area of the drawing sheet designates the backof the case, whereas a portion of the case located in a lower area ofthe drawing sheet designates the front of the case. Reference numeral 1designates a plastic rear case which constitutes the back of the case;and 2 designates a front case which constitutes the front of the case.Reference numeral 3 designates a plane antenna radiation element made ofthin metal plate. Reference 4 designates a power feed terminal; 5 acontact; 6 a circuit board; 7 an LCD; 8 a shield case used for thepurpose of electromagnetic shielding; 9 an RF circuit; 10 an extendabletransmit/receive antenna capable of being housed or extended; 11 aprotuberance used for the purpose of positioning the antenna radiationelement 3; 12 a double-sided table used for fixing the antenna element 3on the internal wall of the rear case 1; 13 designates a power feedland; 14 a digital circuit component; and 15 a replaceable battery.

[0014] The antenna element 3 is formed from a thin metal plate (having athickness of about 0.1 mm) composed of phosphor bronze. The antennaelement 3 is a radiation element having a quarter-wavelength electricallength such as that causes the antenna to resonate in a receiving areaso as to be able to receive an electronic wave transmitted from a basestation, thereby constituting a quarter λ (wavelength) non-contactantenna. Several holes are formed in the antenna radiation element 3,and the positioning protuberance 11 of the rear case 1 is fitted intoone of the holes at the time of assembly of a radio, thereby positioningthe antenna element 3.

[0015] The somewhat large power feed land 13 formed on the circuit board6 is connected to a receiving circuit (not shown) via an unillustratedpower feed circuit and an unillustrated matching circuit. The power feedterminal section 4 is made of electrically conductive material and issoldered to the power feed land 13. The contact 5 comes into anappropriate position of the antenna radiation element 3 under pressure,thereby maintaining conduction of electricity. The reason for this isthat the rear case 1 is assembled or disconnected from the portableradio without difficulties.

[0016] With the foregoing construction, the antenna radiation element 3mounted on the internal wall of the rear case 1 produces resonance withrespect to a ground (or an internal layer) of the circuit board 6positioned below the antenna radiation element 3. The electric powerthus received enters the receiving circuit via the power feed terminal4, the power feed land 13, and the power feed line.

[0017] As can be seen from the foregoing description, the antennaradiation element 3 is not directly positioned on the circuit board 6and is fixedly fitted on the internal wall of the rear case 1 within thearea occupied by the built-in antenna made up of the antenna radiationelement 3 positioned above the circuit board 6. Therefore, only thepower feed terminal 4 of the circuit board 6 is associated with thebuilt-in antenna, and hence the area of the circuit board 6 occupied bythe built-in antenna is considerably reduced. Eventually, the space ofthe circuit board 6 is correspondingly increased. So long as a componenthas a small height such as a digital circuit component 14, any componentcan be positioned on the circuit board 6 immediately below the antennaradiation element 3.

[0018] Since the antenna radiation element 3 uses the internal wall ofthe rear case 1, the element is not subjected to space limits. Becauseof this, the antenna radiation element 3 can be formed into a big size,thereby resulting in an increase in gain.

[0019] Even in the following respects, the increase in the size of theantenna radiation element 3 exerts a good influence on an increase ingain. There is a tendency for gain to increase as the distance betweenthe ground and the radiation element is increased. Since the presentinvention eliminates a gap between the antenna radiation element 3 andthe rear case 2, the distance between the circuit substrate 6 (ground)and the antenna radiation element 3 becomes the maximum height which theportable radio can accomplish, thereby enabling a significant increasein gain. Further, since the antenna radiation element 3 is formed from athin metal plate in the present invention, the gain is prevented frombeing deteriorated by a dielectric loss.

[0020] Further, since the antenna radiation element 3 is formed from ametal plate, the outer shape of the antenna radiation element 3 can beaccurately formed, enabling prevention of irregularities in the outershape.

[0021] The positioning protuberance 11 is formed on the rear case 1 asmeans for positioning the antenna radiation element 3 on the rear case 1in the previous embodiment, and the holes corresponding to thepositioning protuberance 11 are formed in the antenna radiation element3 in order to position the antenna radiation element. However, thepositioning means is not limited to the foregoing holes and theprotuberance. Guide means, such as lines or grooves, may be formed inthe rear case 1 so as to correspond to the outer shape of the antennaradiation element 3.

[0022] Further, the power feed terminal 4 may be a conductor of anyshape, so long as the terminal may electrically connect the antennaradiation element 3 to the power feed land 13. The power feed terminal14 may be formed into a spring or a leaf.

[0023] Finally, because the antenna radiation element 3 is formed from alight-weight thin metal plate, the antenna radiation element 3 is bondedto the internal wall of the rear case 1 by means of the double-sidedtape 12 in the previous embodiment. However, the fixing means is notlimited to the double-sided tape. The antenna radiation element 3 may bebonded to the internal wall by means of an adhesive. Alternatively, thepositioning protuberance 11 may be thermally fused and pushed to therebyextend the size of the protuberance, whereby the antenna radiationelement 3 may be fixed by the protuberance.

[0024] In an example in which the present embodiment is applied to adigital portable telephone which operates in a band of 800 MHz, the areaof the circuit board 6 occupied by the power feed terminal 4 measures5×4 mm (length and width) and is considerably smaller than that requiredby a conventional portable telephone. Since the antenna radiationelement itself utilizes the internal wall of the rear case, the antennaradiation element can be formed to a size of 24 mm×24 mm×7 mm (length xwidth x height from the ground). In contrast with the conventionalantenna radiation element having a limited size, the antenna radiationelement can be formed in large size.

Embodiment 2

[0025]FIG. 2 shows a second embodiment of the present invention. Theelements which are the same as those of the first embodiment will beassigned the same reference numerals, and their explanations will beomitted. As is obvious from FIG. 2, the portable radio according to thesecond embodiment is different from that according to the firstembodiment in the structure of the power feed terminal 4. However, theportable radio according to the second embodiment achieves high gain, asdoes the portable radio according to the first embodiment. In the caseof the portable radio according to the first embodiment shown in FIG. 1,in consideration of mass production of the portable radio, a retainingtool is required to retain the power feed terminal 4 in such a way thatthe power feed terminal 4 can come into contact with the antennaradiation element 3 at the time of assembly of the portable radio. As amatter of course, such a retaining tool occupies a slight area of thecircuit board 6.

[0026] To solve this problem, in the second embodiment, a portion of thethin metal plate forming the antenna radiation element 3 is bent, sothat the power feed terminal 4 is integrally formed. The tip end of thepower feed terminal 4 is further bent so as to form the contact 5. Whenthe circuit board 6 is attached to the rear case 1 at the time ofassembly of a radio, the contact 5 resiliently comes into contact withthe power feed land 13 of the circuit board 6 under pressure and iselectrically connected to the circuit on the circuit board 6.

[0027] As mentioned previously, it is only essential that the power feedterminal 4 be formed by processing a thin metal plate. If a portion ofthe antenna radiation element 3 formed from a thin plane metal plate isbent so as to form the power feed terminal 4, the power feed terminal 4can be formed integrally with the antenna radiation element 3. With sucha construction, both the antenna radiation element and the power feedterminal can be formed from the same material. Since it is only add abending operation to the manufacture of the antenna radiation element,the superior productivity of the portable radio can be achieved. Thepower feed terminal 4 may be formed into any shape, so long as theelectrical connection between the antenna radiation element 3 and thepower feed land 13 is maintained when the rear case 1 is mounted on thecircuit board 6.

[0028] The antenna radiation element 3 can be soldered integrally to thepower feed terminal 4. The power feed terminal 4 may be formed from aconductor of any shape, such as a spring or a leaf spring, so long asthe antenna radiation element 3 can be electrically connected to thepower feed land 12.

[0029] In one example in which the second embodiment is applied to adigital portable telephone which operates in a band of 800 MHz, only thepower feed land 13 occupies the area measuring 6×3 mm (length x width)on the circuit substrate 6 of the built-in antenna. No other constituentelements associated with the antenna radiation element 3 are disposed onthe circuit board 6, thereby minimizing the occupied area of the circuitboard. In comparison with the area occupied by the power feed land 13 inthe first embodiment, the area occupied by the same can be reducedfurther in the second embodiment.

[0030] As mentioned previously, only the power feed land occupies a partof the area of the circuit board, and the need to place otherconstituent elements associated with the built-in antenna on the circuitboard 6 is completely eliminated, thereby effectively reducing the sizeof the portable radio having a built-in antenna.

[0031] As mentioned previously, according to the present invention, itis possible to implement a built-in antenna which occupies a smallerarea of the circuit board of the portable radio and achieves high gain.Further, a built-in antenna is positioned on the internal wall of thecasing of the radio, and other components can be arranged on the circuitboard in the space of the circuit board formed immediately below thebuilt-in antenna. As a result, the size of the circuit board; namely,the size of the portable radio, can be readily reduced.

Embodiment 3

[0032] With regard to a plane antenna housed in a casing of a portableradio, there is formed a quarter λ non-grounding multiple resonanceantenna comprising an antenna radiation element; a branch where one endof a longer radiation element and one end of a shorter radiation elementare connected together; the other ends of the longer and shorterradiation elements which are formed into open ends and are brought intoclose proximity to each other so as to form a gap; and couplingcapacitance which develops in the gap and is used for impedancematching. Power is fed to the branch. Such an antenna radiation elementis positioned on the internal wall of the casing of the portable radio,and the branch of the antenna radiation element is electricallyconnected to the power feed circuit provided on the circuit board withinthe casing. A ground is formed as power feed means in the circuit boardwithin the casing. Power is fed to the branch by the power feed means,so that the antenna radiation element produces multiple resonancebetween the branch and the ground of the circuit board. Further, thepower feed means has resilience and comes into elastic contact with thebranch. In order to place the antenna radiation element in apredetermined position on the internal wall of the casing, antennapositioning means is provided in a predetermined location on theinternal wall of the casing. A protuberance is used as antennapositioning means, and in such a case a hole is formed in the antennaradiation element.

[0033]FIG. 3 is a front view showing the antenna radiation element 3mounted on the rear case 1, which has a branched shape and is made of athin metal plate. Reference numeral 17 designates a longer radiationelement section; 18, a shorter radiation element section; 16, a branchformed by connection of the radiation elements 17 and 18; and 19, a gapas a result of the open ends of the radiation elements 17, 18 coming inproximity to each other.

[0034] The antenna radiation element 3 is formed from a thin metal plate(having a thickness of about 0.1 mm) composed of phosphor bronze. Theantenna radiation element 3 comprises a longer radiation element 17having a length to produce resonance in a lower frequency range of tworeceiving ranges and a short radiation element 18 having a length toproduce resonance in a higher frequency range. One end of each of theradiation elements 17, 18 is connected to the branch 16, and the otherend of each of the radiation elements is open. The antenna radiationelement 3 as a whole has a branched shape, and a plurality of smallholes are formed in the antenna radiation element 3 so as to fittinglyreceive the positioning plastic protuberances 11 formed on the rear casefor the purpose of positioning. As a result of power being fed to thebranch 16, the antenna radiation element is capable of producingmultiple resonance in two receiving ranges so as to be able to receivetwo different waves transmitted from the base station.

[0035] The somewhat large power feed land 13 formed on the circuit board6 is connected to a receiving circuit (not shown) via a power feedcircuit (not shown) and an unillustrated matching circuit. The powerfeed terminal section 4 is made of electrically conductive material andis soldered to the power feed land 13. The contact 5 comes into anappropriate position of the antenna radiation element 3 under pressure,thereby maintaining conduction of electricity. The reason for this isthat the rear case 1 is assembled or disconnected from the portableradio without difficulties. In short, the rear case 1 having the antennaradiation element 3 mounted thereon is attached to the front case 2having the circuit substrate 6 mounted thereon at the time of assembly.The contact 5 of the power feed terminal 4 mounted on the internalcircuit board 6 comes into resilient contact with the branch 16 of theantenna radiation element 3.

[0036] With the foregoing construction, multiple resonance arisesbetween the antenna radiation element 3 mounted on the internal wall ofthe rear case 1 by the double-sided tape 12 produces multiple resonanceand the ground (or an internal layer) of the circuit board 6 positionedbelow the antenna radiation element 3. The electric power thus receivedenters the receiving circuit from the antenna element 3 via the powerfeed terminal 4, the power feed land 13, and the power feed line. Thecoupling capacitance is controlled by adjusting the width of the gapdeveloped when the open end of the longer radiation element 17 isbrought into close proximity to the open end of the shorter radiationelement, thereby achieving optimum impedance matching. As can be seenfrom the foregoing description, the multiple resonance built-in antennaaccording to the present invention can be implemented by a simpleconfiguration in which power is fed to the antenna radiation element 3,which is formed from a thin metal plate into a branched shape, via thebranch 16. Therefore, the antenna can be switched to a singularresonance type antenna to a multiple resonance antenna by changingmerely the shape of the metal plate. Further, the antenna is ofnon-grounding type, and therefore the need for grounding is eliminated.Accordingly, the power-feed structure can be simplified. As a result,the cost of the portable radio is reduced, and the mass-productivity ofthe same is improved.

[0037] The antenna radiation element 3 is not provided on the circuitboard 6 and is fitted on the internal wall of the rear case 1.Consequently, only the power feed terminal is provided on the circuitboard 6, and the need of grounding is eliminated. Therefore, the area ofthe board occupied by the built-in antenna is minimized, and the spaceof the board is increased correspondingly. A component, such as adigital circuit component 14, can be placed on the board immediatelybelow the antenna radiation element 3, so long as the component has asmall height.

[0038] The antenna radiation element 3 utilizes the internal wall of therear case 1, and circuit components do not limit the space for theantenna radiation element 3. The radiation element can be formed intolarge size, thereby resulting in an increase in gain.

[0039] In a portable telephone which is made compact more and more, whenthe long radiation element 17 and the short radiation element 18 aremounted on the internal wall of the rear case of the portable telephone,the radiation elements are positioned close to each other, resulting innoticeable mutual coupling capacitance. The present invention activelyutilizes this coupling capacitance. Even if the radiation elements comeinto close proximity to each other, impedance matching can be ensured byadjusting the gap to an appropriate value.

[0040] The power feed terminal 4 may be a conductor of any shape, solong as the terminal may electrically connect the antenna radiationelement 3 to the power feed land 13. The power feed terminal 14 may beformed into a spring or a leaf.

[0041] In an example in which the present embodiment is applied to adigital portable telephone which operates in a band of 800 MHz, thereare two receiving ranges; namely, a band ranging from 810 to 830 MHz anda band ranging from 870 to 885 MHz. Since the antenna radiation elementutilizes the internal wall of the rear case, the antenna radiationelement can be formed to a size of 24 mm×30 mm×7 mm (length x width xheight from the ground). The area of the circuit board 6 occupied by thepower feed terminal 4 measures 5×4 mm (length and width) and isconsiderably smaller than that required by a conventional portabletelephone. Further, FIG. 4A shows the characteristics of impedancematching obtained when the open end of the longer radiation element anda short radiation element is optimized. If the gap is reduced, the stateof match is changed to such as that shown in FIG. 4B. In contrast, ifthe gap is increased, the state of match is changed to such as thatshown in FIG. 4C.

[0042] The present invention can implement multiple resonance and spacesaving suitable for a portable radio.

What is claimed is:
 1. A portable radio comprising: a case; an antennaradiation element formed from a thin metal plate, said antenna radiationelement being mounted on the internal wall of said case; a circuit boardon which a circuit is provided, said circuit board being attached tosaid case; and a power feed terminal which establishes an electricalconnection between said antenna radiation element and said circuitprovided on the circuit board.
 2. A portable radio as claimed in claim 1, wherein the power feed terminal is fixed on the circuit board inadvance, and the power feed terminal is brought into forced contact withthe antenna radiation element mounted on the internal wall of the casewhen the circuit board is attached to the case.
 3. A portable radio asclaimed in claim 1 , wherein the power feed terminal is integrallyformed with the antenna radiation element beforehand, and the power feedterminal is brought into forced contact with a power feed land formed onthe circuit substrate.
 4. A portable radio as claimed in claim 1 ,wherein a positioning protuberance is provided on the internal wallsurface of the casing to fix the antenna radiation element on theinternal wall of the casing, and positioning holes used for receivingthe protuberance are formed in the antenna radiation element.
 5. Aportable radio as claimed in claim 1 , wherein said antenna radiationelement which includes a branch where one end of a longer radiationelement is connected to one end of a shorter radiation element, and theother ends of the longer and shorter radiation elements which are openends and are positioned in close proximity to each other so as to formgap between them, and wherein impedance matching is accomplished bymeans of the coupling capacitance developed in the gap, and power is fedto the branch.
 6. A plane antenna comprising: an antenna radiationelement which includes a branch where one end of a longer radiationelement is connected to one end of a shorter radiation element, and theother ends of the longer and shorter radiation elements which are openends and are positioned in close proximity to each other so as to formgap between them, wherein impedance matching is accomplished by means ofthe coupling capacitance developed in the gap, and power is fed to thebranch.
 7. A plane antenna as claimed in claim 6 , wherein said antennaradiation element is located on an internal wall of a casing, and acircuit board which is located within the casing and has power feedmeans and the ground, wherein the power feed means feeds power to thebranch to thereby produce multiple resonance between the branch and theground.
 8. A plane antenna as claimed in claim 7 , wherein said powerfeed means is made of elastic member and is brought into contact withthe branch.